This invention relates generally to the field of medical devices and more particularly to a system and method for classifying sensed cardiac complexes.
Effective, efficient ventricular pumping action depends on proper cardiac function. Proper cardiac function, in turn, relies on the synchronized contractions of the heart at regular intervals. When normal cardiac rhythm is initiated at the sinoatrial node, the heart is said to be in sinus rhythm. However, when the heart experiences irregularities in its coordinated contraction, due to electrophysiological disturbances caused by a disease process or from an electrical disturbance, the heart is denoted to be arrhythmic. The resulting cardiac arrhythmia impairs cardiac efficiency and can be a potential life threatening event.
Cardiac arrhythmias occurring in the atrial of the heart are called supraventricular tachyarrhythmias (SVTs). Cardiac arrhythmias occurring in the ventricular region of the heart are called ventricular tachyarrhythmias (VTs). SVTs and VTs are morphologically and physiologically distinct events. VTs take many forms, including ventricular fibrillation and ventricular tachycardia. Ventricular fibrillation is a condition denoted by extremely rapid, nonsynchronous contractions of the ventricles. This condition is fatal unless the heart is returned to sinus rhythm within a few minutes. Ventricular tachycardia are conditions denoted by a rapid heart beat, 150 to 250 beats per minute, that has its origin in some abnormal location within the ventricular myocardium. The abnormal location is typically results from damage to the ventricular myocardium from a myocardial infarction. Ventricular tachycardia can quickly degenerate into ventricular fibrillation.
SVTs also take many forms, including atrial fibrillation and atrial flutter. Both conditions are characterized by rapid uncoordinated contractions of the atria. Besides being hemodynamically inefficient, the rapid contractions of the atria can also adversely effect the ventricular rate. This occurs when the aberrant contractile impulse in the atria are transmitted to the ventricles. It is then possible for the aberrant atrial signals to induce VTs, such as a ventricular tachycardia.
Implantable cardioverter/defibrillators (ICDs) have been established as an effective treatment for patients with serious ventricular tachyarrhythmias. ICDs are able to recognize and treat tachyarrhythmias with a variety of tiered therapies. These tiered therapies range from providing antitachycardia pacing or cardioversion energy for treating tachycardia to defibrillation energy for treating ventricular fibrillation. To effectively deliver these treatments, the ICD must first identify the what type of tachyrhythmia is occurring in the heart.
Attempts at identifying tachyarrhythmias have included comparing the morphologies of individual cardiac complexes to model or template cardiac complexes. Template cardiac complex morphologies are created from cardiac complexes sensed from a signal channel electrogram. Once created, the template cardiac complex morphologies are integrated into morphology algorithms programmed into the ICD. As the ICD encounters a tachycardia episode, cardiac complexes sensed on the single channel electrogram are compared to the template cardiac complex morphologies in the morphology algorithms. Comparing the morphologies of each cardiac complex to the template cardiac complex requires the signals of the two complexes to be positioned over each other. The morphologies of the signals are then analyzed in a time and energy intensive signal shape analysis to determine whether the cardiac complex should be classified as a template cardiac complex.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for providing a reliable system and method for analyzing and classifying cardiac complexes in a more time and energy efficient manner.
As explained in detail below, the present subject matter utilizes cardiac information from two or more cardiac signals to analyze and classify sensed cardiac complexes in a more time and energy efficient manner. The two or more cardiac signals are sensed from two or more locations within, or on, the heart of the patient. A cardiac complex sensed using two or more cardiac signals includes the relative time at which the cardiac complex is sensed in each of the two or more cardiac signals. This additional factor allows for a more efficient comparison to be made between a sensed cardiac complex and a template cardiac complex representing a predetermined cardiac condition. Based on the comparison, the cardiac complex is classified and this information is used to either determine what type of therapy to deliver to a patient or to assess the occurrence of a variety of predetermined cardiac conditions which may be helpful in providing treatment to the patient.
In one embodiment, the present subject matter provides for the monitoring of two or more cardiac signals representative of a patient""s cardiac activity. A cardiac complex is detected in each of the two or more cardiac signals, where the cardiac complex in each of the two or more cardiac signals represents at least a portion of the heart""s cardiac cycle. The morphology of the cardiac complex in each of the two or more cardiac signals is then compared to the morphology of a template cardiac complex. Based on the morphology comparison, the cardiac complex is then classified as either being associated with the template cardiac complex or not being associated with the template cardiac complex.
In one embodiment, a first signal and a second signal representative of electrical cardiac activity are monitored. As the first signal is being monitored it is analyzed to detect the onset of a tachycardia episode. When a tachycardia episode is detected, individual cardiac complexes in the first signal and the second signal are detected and windowed for analysis. Predetermined features are then located in the cardiac complex detected in the first signal and in a first normal sinus rhythm representative complex. In one embodiment, the predetermined features include repeatably identifiable complex sections common to the cardiac complex detected in the first signal and the first NSR representative complex.
The predetermined features located in the first signal and in the first NSR representative complex are then aligned within the analysis window. The cardiac complex detected in the second signal is then compared to a second NSR representative complex to determine whether the cardia complex is an arrhythmic cardiac complex. In one embodiment, the morphology of the second NSR representative complex and the morphology of the cardiac complex detected in the second signal to determine whether the cardia complex is an arrhythmic complex.
In an alternative embodiment, as a cardiac complexes are detected in the first signal and the second signal they are windowed for analysis. Predetermined features are then located in the cardiac complex detected in the first signal and in a first normal sinus rhythm representative complex. Scalar values are then generated as a function of the position, or location, of the predetermined features in each of the cardiac signals. The scalar values are then used to create a cardiac vector which represents the cardiac complex.
The cardiac vector is compared to one or more classification vectors, where each of the one or more classification vectors represents a predetermined cardiac condition. A similarity coefficient is determined for the comparison between the cardiac vector and each of the one or more classification vectors. When a similarity coefficient for the comparison of the cardiac vector and a classification vector exceeds a predetermined threshold, the cardiac complex is classified as the predetermined cardiac condition represented by the classification vector.
Additionally, the cardiac vector can be aligned with a classification vector prior to comparing the two vectors. In one embodiment, the process of aligning includes adjusting each scalar value in the cardiac vector so one of the element positions of the cardiac vector equals a scalar value in a corresponding element position in a classification vector.
In an alternative embodiment, as a cardiac complexes are detected in the first signal and the second signal they are windowed for analysis. The morphology of the cardiac complex in the first cardiac signal and the second cardiac signal is then compared to a first template morphology and a second template morphology, respectively. The cardiac complex is then classified based on the comparison of the morphology of the cardiac complex in the first cardiac signal and the second cardiac signal to the first template morphology and the second template morphology.
These and other features and advantages of the invention will become apparent from the following description of the embodiments of the invention.